Electrochemical cells and use thereof

ABSTRACT

Electrochemical cells comprise
         (A) at least one cathode comprising at least one lithiated Mn-containing compound having an Mn content of from 60 to 80 mol %, based on transition metal in cathode (A),   (B) at least one anode comprising carbon in electrically conductive form,   (C) at least one electrolyte comprising   (a) at least one aprotic organic solvent,   (b) at least one lithium salt, and   (c) at least one organic compound having at least one Si—N single bond per molecule.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic construction of a disassembled electrochemicalcell for testing inventive mixtures.

FIG. 2 shows a capacity vs cycle number for EZ.1 (curve b) and V-EZ.2(curve a).

The present invention relates to electrochemical cells comprising

-   -   (A) at least one cathode comprising at least one lithiated        Mn-containing compound having an Mn content of from 60 to 80 mol        %, based on transition metal in cathode (A),    -   (B) at least one anode comprising carbon in electrically        conductive form,    -   (C) at least one electrolyte comprising        -   (a) at least one aprotic organic solvent,        -   (b) at least one lithium salt, and        -   (c) at least one organic compound having at least one Si—N            single bond per molecule.

The search for ways to store electric energy efficiently has been goingon for years. Efficient storage of electric energy would allow electricenergy to be generated when it is advantageous and used when needed.

Accumulators, for example lead accumulators and nickel-cadmiumaccumulators, have been known for many decades. The known leadaccumulators and nickel-cadmium accumulators have the disadvantages,however, of a comparatively low energy density and of a memory effectwhich reduces the rechargeability and hence the useful life of leadaccumulators and nickel-cadmium accumulators.

Lithium ion accumulators, frequently also referred to as lithium ionbatteries, are used as an alternative. They provide higher energydensities than accumulators based on lead or comparatively noble heavymetals.

Since many lithium ion batteries utilize metallic lithium or lithium inoxidation state 0, or produce it as an intermediate, they are watersensitive. Moreover, the electrolytes used, for example LiFP₆, are watersensitive during long-term operation. Water is therefore out of thequestion as a solvent for the lithium salts used in lithium ionbatteries. Instead, organic carbonates, ethers and esters are used assufficiently polar solvents. The literature accordingly recommends usingwater-free solvents for the electrolytes, see for example WO2007/049888.

Water-free solvents, however, are inconvenient to produce and process.Numerous solvents inherently useful for lithium ion batteries comprisein the order of 100 ppm or more of water. However, such high proportionsof water are unacceptable for most lithium ion batteries. The problem ofproviding sufficiently suitable solvents for lithium ion batteries iscomplicated by the fact that most state of the art lithium ion batteriescomprise not a single solvent but solvent mixtures of which some differgreatly in their activity with driers.

U.S. Pat. No. 6,235,431 proposes adding compounds having Si—N bonds asan additive to the solvent (mix) in a lithium ion battery. This compoundreacts with water and thereby protects not only the conducting salt butalso the cathode material. U.S. Pat. No. 6,235,431 specificallyrecommends organosilazanes and organodisilazanes as well ashexamethylcyclotrisilazane. It was observed, however, that compounds ofthis type can react with water to form ammonia or volatile organicamines which are capable of damaging a lithium ion battery in prolongedoperation thereof.

Electrochemical cells are known where the cathode material comprisesmanganese-rich materials wherein the lithium deintercalation takes placeessentially at high potentials. High voltages for the purposes of thisinvention are voltages above 4.5 volts, based on the potential ofmetallic lithium. Particularly high energy densities are obtained whencathode materials of this type are used in conjunction with carbonanodes. Useful carbon anodes include for example anodes comprisinggraphite, partially or fully amorphous particles of carbon. Knownelectrochemical cells based on these materials have aging propertiesthat are insufficient for many possible areas of use, especially in themotor vehicle sector. For instance, a severe decrease in capacity isobserved on repeatedly charging and discharging cells of this type, seefor example D. Aurbach et al., J. Power Sci. 2006, 162, 780.

The present invention has for its object to provide electrochemicalcells that have good performance characteristics and, more particularly,are readily cyclable without displaying adverse signs of aging.

We have found that this object is achieved by the electrochemical cellsdefined at the beginning.

For the purposes of the present invention, lithium ion accumulators arealso referred to as lithium ion batteries.

Electrochemical cells of the present invention comprise

-   (A) at least one cathode, also called cathode (A) for short,    comprising at least one lithiated Mn-containing compound having an    Mn content of at least 60 to 80 mol %, based on transition metal in    cathode (A),-   (B) at least one anode, also called anode (B) for short, comprising    carbon in electrically conductive form,-   (C) at least one electrolyte comprising    -   (a) at least one aprotic organic solvent, also called        solvent (a) for short,    -   (b) at least one lithium salt, also called lithium salt (b) for        short,    -   (c) at least one organic compound having at least one Si—N        single bond per molecule, also called compound (c) for short.

Cathode (A), anode (B) and electrolyte (C) will now be more particularlydescribed.

The lithium-containing compound present in cathode (A) is selected fromlithium-containing transition metal mixed oxides of layered structure,lithiated transition metal mixed oxides of spinel structure andlithiated transition metal phosphates of olivine structure, for exampleLiMn_(1-h)Fe_(h)PO₄ (where 0.2≦h≦0.4). Suitable transition metal mixedoxides of layered structure are especially those of the general formula

Li_((1+y))[Ni_(a)Co_(b)Mn_(c)]_((1−y))O₂

where y is selected from zero to 0.3 and preferably from 0.05 to 0.2,c is from 0.6 to 0.8, a and b may each be the same or different and arein the range from 0.0 to 0.4, subject to the proviso:

a+b+c=1

Suitable transition metal mixed oxides of spinel structure areespecially those of the general formula (I)

Li_(1+t)M_(2−t)O_(4-d)  (I)

whered is from zero to 0.4,t is from zero to 0.4,while from 60 to 80 mol % of M is manganese. Further M's, from which notmore than 40 mol % is chosen, are one or more metals from groups 3 to 12of the periodic table, for example Ti, V, Cr, Fe, Co, Ni, Zn, Mo, withpreference being given to Co and Ni, and especially Ni.

In this connection, the phrase “transition metal in cathode (A)” is tobe understood as meaning the entire transition metal comprised in thecathode material irrespective of the oxidation state, but not currentcollectors which may comprise transition metal.

In one embodiment of the present invention, at least one cathode (A)comprises a cathodic active material having a manganese content rangingfrom 60 to 80 mol % and preferably from 73 to 78 mol %, based ontransition metal in cathode (A).

In one embodiment of the present invention, lithiated Mn-containingcompound is selected from LiNi_(0.25)Mn_(0.75)O₄, LiNi_(0.24)Mn_(0.76)O₄and LiNi_(0.26)Mn_(0.74)O₄.

Cathode (A) may further comprise for example carbon in electricallyconductive form, for example as carbon black, graphite, graphene or ascarbon nanotubes.

Cathode (A) may further comprise for example a binder, for example apolymeric binder. Particularly suitable polymeric binders arepolyvinylidene fluoride (PVdF), polytetrafluoroethylene, copolymers oftetrafluoroethylene and hexafluoropropylene, copolymers oftetrafluoroethylene and vinylidene fluoride and polyacrylonitrile.

Electrochemical cell of the present invention comprises at least oneanode (B).

In one embodiment of the present invention, at least one anode (B)comprises carbon in an electrically conductive form, for example carbonblack, what is known as hard carbon, i.e., graphite-like carbon withlarger amorphous regions than graphite has, or preferably graphite.

Electrochemical cell of the present invention comprises at least oneelectrolyte (C) comprising

-   -   (a) at least one aprotic organic solvent,    -   (b) at least one lithium salt, and    -   (c) at least one organic compound having at least one Si—N        single bond per molecule.

Electrolyte (C) is liquid under standard conditions (1 bar, 0° C.) andpreferably also at 1 bar and −15° C.

Electrolyte (C) comprises at least one aprotic solvent (a), preferablyat least two aprotic solvents (a) and more preferably at least threeaprotic solvents (a). Aprotic solvent (a) is generally an organicsolvent.

In one embodiment of the present invention, electrolyte (C) may compriseup to ten different aprotic solvents (a).

For the purposes of the present invention, aprotic organic solvents (a)are not just those aprotic solvents that are liquid at room temperature.

The present invention also comprises aprotic organic compounds which aresolid at room temperature as pure compound, but which are liquid inadmixture with the remaining aprotic organic solvents. Ethylenecarbonate may be mentioned by way of example in that it is liquid withinwide limits when in a mixture with diethyl carbonate and/or methyl ethylcarbonate, but as a pure substance has a melting point of about 36° C.

In one embodiment of the present invention, aprotic organic solvent (a)is selected from

(i) cyclic and noncyclic organic carbonates,(ii) di-C₁-C₁₀-alkyl ethers,(iii) di-C₁-C₄-alkyl-C₂-C₆-alkylene ethers,(iv) cyclic ethers,(v) cyclic and acyclic acetals and ketals,(vi) orthocarboxylic esters, and(vii) cyclic and noncyclic carboxylic esters.

In one preferred embodiment of the present invention, aprotic organicsolvent (a) is selected from

(i) organic carbonates, cyclic or acyclic,(ii) di-C₁-C₁₀-alkyl ethers,(iii) di-C₁-C₄-alkyl-C₂-C₆-alkylene ethers, and(v) cyclic and acyclic acetals and ketals.

Examples of preferred noncyclic organic carbonates (i) aredi-C₁-C₄-alkyl carbonates where C₁-C₄-alkyl may be the same or differentand is selected from C₁-C₄-alkyl, for example methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl, preferably methyl or ethyl.

Particularly preferred noncyclic organic carbonates (i) are dimethylcarbonate, diethyl carbonate and methyl ethyl carbonate and mixturesthereof, i.e., mixtures of at least two of the recited compoundsdimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

Examples of preferred cyclic organic carbonates (i) are those of thegeneral formula (V a) and (V b)

where R⁸ is selected C₁-C₄-alkyl, for example methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl, preferably methyl,fluorine, mono- or polyfluorinated C₁-C₄-alkyl, for example CF₃ orn-C₄H₉, and especially hydrogen.

Preferred cyclic organic carbonate (i) is further difluoroethylenecarbonate,

Examples of preferred di-C₁-C₁₀-alkyl ethers (ii) are diethyl ether,diisopropyl ether and di-n-butyl ether.

Examples of di-C₁-C₄-alkyl-C₂-C₆-alkylene ethers (iii) are1,2-dimethoxyethane, 1,2-diethoxyethane, diethylene glycol dimethylether, triethylene glycol dimethyl ether, tetraethylene glycol dimethylether and diethylene glycol diethyl ether.

Examples of cyclic ethers (iv) are 1,4-dioxane and tetrahydrofuran(THF).

Examples of acyclic acetals and ketals (v) are 1,1-dimethoxyethane and1,1-diethoxyethane.

Examples of cyclic acetals and ketals (v) are 1,3-dioxolane and1,3-dioxane.

Examples of orthocarboxylic esters (vi) are tri-C₁-C₄-alkylorthoformates, especially trimethyl orthoformate and triethylorthoformate.

Examples of carboxylic esters (vii) are ethyl acetate and methylbutyrate and also dicarboxylic esters, for example dimethyl malonate.γ-Butyrolactone is an example of a cyclic carboxylic ester (lactone).

In one specific embodiment of the present invention, mixture accordingto the present invention comprises noncyclic organic carbonate(s) andcyclic organic carbonate(s) in a weight ratio of 1:10 to 10:1 andpreferably 3:1 to 1:1.

Electrolyte (C) further comprises at least one lithium salt (b). Lithiumsalts (b) are preferably salts of monovalent anions. Examples ofsuitable lithium salts (b) are LiPF₆, LiBF₄, LiClO₄, LiAsF₆, LiCF₃SO₃,LiC(C_(x)F₂x+1SO₂)₃, lithium bisoxalatoborate, lithiumdifluorobisoxalatoborate, lithium imides such as LiN(C_(x)F_(2x+1)SO₂)₂,where x is an integer from 1 to 20, LiN(SO₂F)₂, Li₂SiF₆, LiSbF₆,LiAlCl₄, and salts of the general formula (C_(x)F_(2x+1)SO₂)_(m)XLi,where x is as defined above and m is as defined below:

m=1, when X is selected from oxygen and sulfur,m=2, when X is selected from nitrogen and phosphorus, andm=3, when X is selected from carbon and silicon.

Particularly preferred lithium salts (b) are selected from LiPF₆, LiBF₄,LiSbF₆, LiBOB, LDFOB and LiPF₃(CF₂CF₃)₃ (LiFAP).

Electrolyte (C) further comprises

-   (c) at least one organic compound having at least one Si—N single    bond per molecule, called compound (c) for short. Compound (c) may    be cyclic or acyclic.

Examples of acyclic compounds (c) are those of the general formula (VI)and (VII)

where the variables are defined as follows:R¹ in each occurrence is different or preferably the same and selectedfrom

-   -   C₁-C₁₀-alkyl, for example methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,        sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,        isohexyl, sec-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl; more        preferably C₁-C₄-alkyl such as methyl, ethyl, n-propyl,        isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl and even        more preferably methyl,    -   C₁-C₁₀-alkoxy, preferably C₁-C₄-n-alkoxy, for example ethoxy,        n-propoxy, n-butoxy and especially methoxy,    -   C₃-C₁₀-cycloalkyl, for example cyclopropyl, cyclobutyl,        cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl,        cyclodecyl, cycloundecyl and cyclododecyl; preference is given        to cyclopentyl, cyclohexyl and cycloheptyl,    -   benzyl and    -   C₆-C₁₄-aryl, for example phenyl, 1-naphthyl, 2-naphthyl,        1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl,        3-phenanthryl, 4-phenanthryl and 9-phenanthryl, preferably        phenyl, 1-naphthyl and 2-naphthyl and more preferably phenyl,    -   each unsubstituted or substituted one or more times with        C₁-C₄-alkyl, especially methyl or isopropyl, or with benzyl or        phenyl,    -   examples of substituted phenyl being for example        para-methylphenyl, 2,6-dimethylphenyl and para-biphenyl.        R² is selected from COOR⁷, for example COOCH₃, COOC₂H₅,    -   C₁-C₁₀-alkyl, for example methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,        sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,        isohexyl, sec-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl; more        preferably C₁-C₄-alkyl such as methyl, ethyl, n-propyl,        isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl and even        more preferably methyl, ethyl or isopropyl,    -   C₂-C₁₀-alkenyl, especially vinyl, 1-allyl, 2-allyl and        homoallyl,    -   C₃-C₁₀-cycloalkyl, for example cyclopropyl, cyclobutyl,        cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl,        cyclodecyl, cycloundecyl and cyclododecyl; preference is given        to cyclopentyl, cyclohexyl and cycloheptyl,    -   benzyl,    -   C₆-C₁₄-aryl, for example phenyl, 1-naphthyl, 2-naphthyl,        1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl,        3-phenanthryl, 4-phenanthryl and 9-phenanthryl, preferably        phenyl, 1-naphthyl and 2-naphthyl and more preferably phenyl,    -   each unsubstituted or substituted one or more times with        C₁-C₄-alkyl, especially methyl or isopropyl, or with benzyl or        phenyl,        R³ is selected from    -   C₁-C₁₀-alkyl, for example methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,        sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,        isohexyl, sec-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl; more        preferably C₁-C₄-alkyl such as methyl, ethyl, n-propyl,        isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl and even        more preferably methyl,    -   C₃-C₁₀-cycloalkyl, for example cyclopropyl, cyclobutyl,        cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl,        cyclodecyl, cycloundecyl and cyclododecyl; preference is given        to cyclopentyl, cyclohexyl and cycloheptyl,    -   benzyl,    -   C₆-C₁₄-aryl, for example phenyl, 1-naphthyl, 2-naphthyl,        1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl,        3-phenanthryl, 4-phenanthryl and 9-phenanthryl, preferably        phenyl, 1-naphthyl and 2-naphthyl and more preferably phenyl,    -   each unsubstituted or substituted one or more times with        C₁-C₄-alkyl, especially methyl or isopropyl, or with benzyl or        phenyl,    -   and especially hydrogen.

Preference is given to cyclic compounds, for example of the generalformula (VIII),

and especially of the general formulae (I) or (II)

where R¹ and R² are each as defined above. The remaining variables aredefined as follows:R³ and R⁴ are each different or preferably the same and selected from

-   -   C₁-C₁₀-alkyl, for example methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,        sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,        isohexyl, sec-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl; more        preferably C₁-C₄-alkyl such as methyl, ethyl, n-propyl,        isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl and even        more preferably methyl,    -   C₃-C₁₀-cycloalkyl, for example cyclopropyl, cyclobutyl,        cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl,        cyclodecyl, cycloundecyl and cyclododecyl; preference is given        to cyclopentyl, cyclohexyl and cycloheptyl,    -   benzyl,    -   C₆-C₁₄-aryl, for example phenyl, 1-naphthyl, 2-naphthyl,        1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl,        3-phenanthryl, 4-phenanthryl and 9-phenanthryl, preferably        phenyl, 1-naphthyl and 2-naphthyl and more preferably phenyl,    -   each unsubstituted or substituted one or more times with        C₁-C₄-alkyl, especially methyl or isopropyl, or with benzyl or        phenyl,    -   and especially hydrogen,        or >C(R³)₂ is a >C═O group.

Examples of preferred >C(R³)₂ are further CHC₆H₅, CH(CH₃), C(CH₃)₂ andespecially CH₂.

Preferably, R³ and R⁴ are each pairwise the same and selected fromhydrogen and methyl.

-   X in each occurrence is different or the same and selected from    oxygen, sulfur, N—R⁵ and C(R⁶)₂, where-   R⁵ is selected from    -   C₁-C₁₀-alkyl, for example methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,        sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,        isohexyl, sec-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl; more        preferably C₁-C₄-alkyl such as methyl, ethyl, n-propyl,        isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl and even        more preferably methyl,    -   C₃-C₁₀-cycloalkyl, for example cyclopropyl, cyclobutyl,        cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl,        cyclodecyl, cycloundecyl and cyclododecyl; preference is given        to cyclopentyl, cyclohexyl and cycloheptyl,    -   benzyl and    -   C₆-C₁₄-aryl, each unsubstituted or substituted one or more times        with C₁-C₄-alkyl, especially methyl or isopropyl, or with benzyl        or phenyl,-   R⁶ in each occurrence is the same or preferably different and    selected from    -   hydrogen and    -   C₁-C₁₀-alkyl, for example methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl,        sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl, n-hexyl,        isohexyl, sec-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl; more        preferably C₁-C₄-alkyl such as methyl, ethyl, n-propyl,        isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl and even        more preferably methyl,    -   C₃-C₁₀-cycloalkyl, for example cyclopropyl, cyclobutyl,        cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl,        cyclodecyl, cycloundecyl and cyclododecyl; preference is given        to cyclopentyl, cyclohexyl and cycloheptyl,    -   benzyl and    -   C₆-C₁₄-aryl, each unsubstituted or substituted one or more times        with C₁-C₄-alkyl, especially methyl or isopropyl, or with benzyl        or phenyl,    -   each unsubstituted or substituted one or more times with        C₁-C₄-alkyl, benzyl or phenyl,-   R⁷ is selected from C₁-C₄-alkyl, such as methyl, ethyl, n-propyl,    isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl and very    particularly preferably methyl, ethyl and isopropyl,-   n is an integer from 1 to 3, preferably 1 or 2 and especially 1.

It is particularly preferable for X to be selected from CHCH₃ andCH(CH₂CH₃).

When, in compounds of formula (II), n=1, then the formula corresponds tothe general formula (II′)

and there is no actual group X.

In one preferred embodiment of the present invention, compound (C) isselected from compounds of the general formulae (I a), (I b), (II a) and(II b),

-   R¹ in each occurrence is different or the same and selected from    -   C₁-C₄-alkyl, such as methyl, ethyl, n-propyl, isopropyl,        n-butyl, isobutyl, sec-butyl and tert-butyl, very particularly        preferably methyl,    -   C₁-C₄-alkoxy, such as ethoxy, n-propoxy, isopropoxy, n-butoxy        and especially methoxy,    -   and phenyl,-   R² is selected from C₁-C₄-alkyl, such as methyl, ethyl, n-propyl,    isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl, very    particularly preferably methyl and tert-butyl,    -   COOCH₃, COOC₂H₅,    -   C₂-C₃-alkenyl, for example —CH═CH₂, —CH₂—CH═CH₂, (E)-CH═CH—CH₃        and (Z)-—CH═CH—CH₃,    -   and phenyl,-   R⁶ in each occurrence is the same or preferably different and    selected from hydrogen and methyl.

In one preferred embodiment of the present invention, compound (C) isselected from the following compounds:

(CH₃)₃Si—N(CH₃)₂, (CH₃)₃Si—N(C₂H₅)₂, (CH₃)₃Si—NHC(CH₃)₃,(CH₃)₃Si—NH(CH₂C₆H₅), (CH₃)₃Si—N(iso-C₃H₇)₂.

Electrolyte (C) may further

from zero to 30 ppm of water, preferably from 3 to 25 ppm and morepreferably at least 5 ppm. Here ppm is always weight ppm (parts permillion), based on total electrolyte.

The proportions of water can be determined by various methods known perse. Karl Fischer titration to DIN 51777 or ISO760: 1978 for example isparticularly suitable. By “zero ppm of water” is meant that the wateramounts are below the detection limit.

Electrolyte (C) may further comprise at least one additive, also calledadditive (d) for short. Additives (d) may be for example: aromaticcompounds, sultones, cyclic exo-methylene carbonates, lithiumbisoxalatoborate (LiBOB) and lithium (difluorooxalato)borate (LiDFOB).

Examples of aromatic compounds suitable as additive (d) are biphenyl,cyclohexylbenzene and 1,4-dimethoxybenzene.

Sultones may be substituted or unsubstituted. Examples of suitablesultones are butanesultone and propylenesultone (propanesultone),formula (IX),

and particularly sultones having at least one C—C double bond permolecule. An example of a substituted sultone is1-phenyl-1,3-butanesultone.

Examples of exo-methylene ethylene carbonates useful as additive (d) areparticularly compounds of general formula (X)

where in each case R⁹ and R¹⁰ can be different or the same and areselected from C₁-C₁₀-alkyl and hydrogen. In one preferred embodiment, R⁹and R¹⁰ are both methyl. In another preferred embodiment of the presentinvention, R⁹ and R¹⁰ are both hydrogen.

Additives (d) may further be cyclic or acyclic alkanes which preferablyhave a boiling point of at least 36° C. as pure substances and at apressure of 1 bar. Examples are cyclohexane, cycloheptane andcyclododecane. It is further possible to use organic esters of inorganicacids, for example methyl ester or ethyl ester of phosphoric acid orsulfuric acid.

In one embodiment of the present invention, electrolyte (C) contains nofurther components beyond aprotic organic solvent (a), lithium salt (b),compound (c), water and optional additive (d).

In one embodiment of the present invention, electrolyte (C) has thefollowing composition:

-   -   (a) altogether from 50 to 99.5 wt %, preferably from 60 to 95 wt        % and more preferably from 70 to 90 wt % of aprotic organic        solvent (a),    -   (b) from 0.1 to 25 wt % and preferably from 5 to 18 wt % of        lithium salt (b),    -   (c) from 0.01 to 5 wt %, preferably 0.08 to 3 wt % and more        preferably 0.15 to 2 wt % of compound (c),    -   (d) altogether zero to altogether 10 wt %, preferably 0.01 to 5        wt % and more preferably 0.4 to 2 wt % of additive(s) (d), and    -   (e) zero to 50 ppm, preferably 3 to 25 ppm and more preferably        at least 5 ppm of water,        wherein recitations in wt % and ppm are each based on total        electrolyte (C).

Lithium ion batteries according to the present invention may furthercomprise customary constituents, for example one or more separators, oneor more current collector platelets and a housing.

Electrolytes (C) used according to the present invention are obtainablefor example as follows:

(α) providing at least one aprotic organic solvent (a), called step (α)for short,(β) optionally mixing with at least one further aprotic organic solvent(a), also called step (β) for short, to obtain a mixture that is liquidat standard conditions,(γ) optionally mixing with one or more additives (d), called step (γ)for short,(δ) drying, called step (δ) for short, and(ε) mixing with compound (c) and optionally with at least one additive(d) and optionally with at least one lithium salt (b), called step (ε)for short.

Steps (α) to (ε) may be carried out in the aforementioned order or insome other order. It is possible for instance to adhere essentially tothe aforementioned order of steps (α) to (ε), but to perform step (δ)immediately before step (γ).

Another version comprises adhering essentially to the aforementionedorder of steps (α) to (ε), but to perform step (γ) directly before step(β).

Solvent (a), additives (d), compound (c) and lithium salts (b) aredefined above.

Steps (α) to (ε) will now be more particularly described.

Mixing solvent (a), compound (c), lithium salt (b) and optionallyadditive (d) can be done at any desired temperature.

Step (α):

One or more solvents (a) are provided. Individual solvents (a) or allsolvents (a) may be provided in the dried state, for example with awater content of 1 to 50 ppm, or with a higher water content.

Steps (β), (γ) and (ε): Mixing Steps

One embodiment of the present invention comprises mixing in each case attemperatures ranging from 10 to 100° C. and more preferably at roomtemperature.

One embodiment of the present invention comprises mixing at atemperature of at least 1° C. above the melting point of thehighest-melting solvent (a).

The upper temperature limit for mixing is determined by the volatilityof the most volatile solvent (a). Preference is given to mixing at atemperature below the boiling point of the most volatile solvent (a).

Mixing can be done at any desired pressure, and atmospheric pressure ispreferred. The duration of mixing can be chosen for example in the rangefrom 5 minutes up to 24 hours.

Step (β) comprises choosing the quantitative ratios of solvent(s) (a)such that a mixture that is liquid at room temperature is obtained.Preference is given to choosing the quantitative ratios of solvent(s)(a) such that a mixture that is liquid at 0° C. is obtained. Particularpreference is given to choosing the quantitative ratios of solvent(s)(a) such that a mixture that is liquid at −15° C. is obtained.Examination as to whether the mixture from step (β) is liquid can beeffected for example through simple optical inspection, for examplethrough visual inspection.

The melting point of a mixture can be lowered by adding diethylcarbonate or methyl ethyl carbonate for example.

Mixing preferably takes place under anhydrous conditions, i.e., underexclusion of air and especially under exclusion of moisture, for exampleunder dry air. Mixing preferably takes place under air exclusion (inertconditions), for example under dry nitrogen or dry noble gas.

Step (δ):

Step (δ) comprises drying. Drying can take place after or preferablybefore addition of compound of general formula (I) or (II), optionallyof additive(s) (d) and optionally of lithium salt(s) (b).

Drying can be effected in a conventional manner over a drier, preferablyover molecular sieves. Molecular sieves are preferably chosen fromnatural and synthetic zeolites which can be in the form of spheres(beads), powders or rods. Preference is given to using 4 Å molecularsieve and more preferably 3 Å molecular sieve.

The actual drying can be effected for example by stirring above thedrier(s).

Preference is given to letting molecular sieve act on solvent (a) in theabsence of chemical driers. Chemical driers for the purposes of thepresent invention are strongly acidic, alkaline or strongly reducingdriers, more particularly selected from low molecular weight compounds,salts and elements. Known acidic driers include for example aluminumalkyls such as for example trimethylaluminum, also phosphorus pentoxideand concentrated sulfuric acid. Known basic driers include for examplepotassium carbonate and CaH₂. Known reducing driers include for exampleelemental sodium, elemental potassium and sodium-potassium alloy.

One embodiment of the present invention comprises conducting step (δ) ata temperature in the range from 15 to 40° C. and preferably in the rangefrom 20 to 30° C.

In one embodiment of the present invention, the time for which molecularsieve is allowed to act in step (δ) is in the range from a few minutes,for example at least 5 minutes, to several days, preferably not morethan 24 hours and more preferably in the range from 1 to 6 hours.

During the practice of step (δ) a little solvent mixture can be removedone or more times in order that the progress of drying may be tracked bymeans of Karl Fischer titration.

It is preferable to keep the stirring or shaking to a minimum.Excessively vigorous stirring/shaking can lead to partial disintegrationof the molecular sieve, and this may give rise to problems with removalby filtration.

This is followed by removing the drier(s), for example by distilling thesolvent(s) (a) off and especially by decanting or filtration.

The present invention further provides for the use of electrochemicalcells of the present invention in lithium ion batteries. Moreparticularly, electrochemical cells of the present invention are usefulin lithium ion batteries wherein a potential difference of at least 4.5volts is reached between at least one anode and at least one cathode atleast temporarily during the production and/or use of theelectrochemical cell in question.

In one embodiment of the present invention, electrochemical cells of thepresent invention are used for driving motor vehicles alone or combinedwith an internal combustion engine.

In another embodiment of the present invention, electrochemical cells ofthe present invention are used for energy storage in electricaltelecommunications equipment.

The present invention further provides a process for producingelectrochemical cells of the present invention. Electrochemical cells ofthe present invention are obtainable for example by a cathode (A) and ananode (B) being combined with each other in a receptacle and admixedwith electrolyte (C). Housings for example are useful as receptacle. Itwill be appreciated that at the same time as or after the combining ofcathode (A) and anode (B) an operation may be carried out for combiningwith other battery constituents, for example with one or more separatorsor one or more current collector platelets.

The admixing with electrolyte (C) is performable for example by fillinginitially or subsequently. In one preferred version, the admixing withelectrolyte is preceded by the internal pressure of the cell in questionbeing lowered to values below 25 000 Pa (pascal).

The invention is elucidated by working examples.

The electrodes used were as follows in all cases:

Cathode (A.1): a lithium-nickel-manganese-spinel electrode was used, itwas prepared as follows. The following were mixed together:

85% of LiMn_(1.5)Ni_(0.5)O₄

6% of PVdF, commercially available as Kynar Flex® 2801 from ArkemaGroup,6% of carbon black, BET surface area 62 m²/g, commercially available as“Super P Li” from Timcal,3% of graphite, commercially available as KS6 from Timcal;

in a screw-top vessel. Sufficient N-methylpyrrolidone (NMP) was addedunder agitation to obtain a viscid paste without lumps. Stirring wasdone for 16 hours.

The paste thus obtained was then blade coated onto aluminum foil 20 μmin thickness and dried in a vacuum drying cabinet at 120° C. for 16hours. Coating thickness after drying was 30 μm. Circular segments werethen die cut out with a diameter of 12 mm.

Anode (B.1): The following were mixed together:

91% of ConocoPhillips C5 graphite6% of PVdF, commercially available as Kynar Flex®2801 from Arkema Group,3% of carbon black, BET surface area 62 m²/g, commercially available as“Super P Li” from Timcal,in a screw-top vessel. Sufficient NMP was added under agitation toobtain a viscid paste without lumps. Stirring was done for 16 hours.

The paste thus obtained was then blade coated onto copper foil 20 μm inthickness and dried in a vacuum drying cabinet at 120° C. for 16 hours.Coating thickness after drying was 35 μm. Circular segments were thendie cut out with a diameter of 12 mm.

The test cell used had a construction as per FIG. 1. On assembly of thecell, it was assembled in the upward direction of the schematic FIG. 1.FIG. 1 has the anode side at the top and the cathode side at the bottom.

The annotations in FIG. 1 mean:

-   -   1, 1′ die    -   2, 2′ nut    -   3, 3′ sealing ring—two in each case; the second, somewhat        smaller sealing ring in each case is not shown here    -   4 spiral spring    -   5 current collector made of steel    -   6 housing

Cathode (A-1) was applied atop the die of cathode side 1′. A separatorcomposed of glass fiber, thickness of separator: 0.5 mm, was then laidatop cathode (A-1). The mixture to be tested was drizzled onto theseparator. Anode (B-1) was placed on the drenched separators. Currentcollector 5 took the form of a stainless steel platelet applied directlyto the anode. Then, the seals 3 and 3′ were added and the components ofthe test cell were screwed together. The steel spring configured asspiral spring 4 and the pressure produced by the threaded union withanode die 1 ensured electrical contact.

II.1 Producing an Inventive Electrochemical Cell EZ.1 and Testing

Whatman (GF/D) was used as separator and drizzled for this purpose withelectrolyte in an argon-filled glove box and positioned between acathode (A-1) and an anode (B-1), so that both the anode and the cathodewere in direct contact with the separator. Electrolyte E-1 was added toobtain inventive electrochemical cell EZ.1.

The test mixture used as E-1 (“electrolyte”) was:

1 M LiPF₆, dissolved in ethylene carbonate and ethyl methyl carbonate ina mass ratio of 1:1, and 2 wt % of compound (I a.1), based on sum totalof LiPF₆, ethylene carbonate and ethyl methyl carbonate.

For this a mixture of ethylene carbonate and ethyl methyl carbonate(1:1, see above) was dried over molecular sieves. Then, compound (I a.1)was dissolved in the mixture. This was followed by further drying overmolecular sieves and the addition of LiPF₆ to obtain electrolyte E-1(“electrolyte”).

E-1 comprised 10 ppm of water, determined by Karl Fischer titration toDIN 51777 or ISO760: 1978 with coulometric detection.

The test was repeated but with an electrolyte solution comprising no (Ia.1) to obtain electrochemical comparative cell V-EZ.2.

II. Electrochemical Characterization of Cell:

The electrochemical investigations on EZ.1 and V-EZ.2 were carried outbetween 4.25 V and 4.8 V.

The first two cycles were run at 0.2 C rate for forming; cycles No. 3 toNo. 50 were cycled at 1 C rate, followed again by 2 cycles at 0.2 Crate, followed by 48 cycles at 1 C rate, etc. The cell wascharged/discharged using an MACCOR Battery Tester at room temperature.

It was possible to show that battery capacity remained very stablethroughout repeated charging and discharging.

The results are depicted in FIG. 2.

We claim:
 1. An electrochemical cell comprising (A) at least one cathodecomprising at least one lithiated Mn-containing compound having an Mncontent of from 60 to 80 mol %, based on transition metal in cathode(A), (B) at least one anode comprising carbon in electrically conductiveform, (C) at least one electrolyte comprising (a) at least one aproticorganic solvent, (b) at least one lithium salt, (c) at least one organiccompound having at least one Si—N single bond per molecule.
 2. Theelectrochemical cell according to claim 1 wherein said lithiatedMn-containing compound is a lithiated Mn-containing spinel.
 3. Theelectrochemical cell according to claim 1 or 2 wherein said lithiatedMn-containing compound is a compound of the general formula (I)Li_(1+t)M_(2−t)O_(4-d)  (I) where d is from zero to 0.4, t is from zeroto 0.4, M is two or more metals from groups 3 to 12 of the periodictable, wherein more than 60 mol % of M is manganese.
 4. Theelectrochemical cell according to any one of claims 1 to 3 wherein saidanode (B) is selected from graphite anodes.
 5. The electrochemical cellaccording to any one of claims 1 to 4 wherein said aprotic organicsolvent (a) is selected from organic carbonates (cyclic or acyclic),di-C₁-C₁₀-alkyl ethers, di-C₁-C₄-alkyl-C₂-C₆-alkylene ethers, and cyclicand acyclic acetals and ketals.
 6. The electrochemical cell according toany one of claims 1 to 5 wherein said organic compound (c) is selectedfrom compounds of the general formula (II), (III) and (IV):

where R¹ in each occurrence is the same or different and selected fromC₁-C₁₀-alkyl, C₁-C₁₀-alkoxy, C₃-C₁₀-cycloalkyl, benzyl and C₆-C₁₄-aryl,each unsubstituted or substituted one or more times with C₁-C₄-alkyl,benzyl or phenyl, R² is selected from COOR⁸, C₁-C₁₀-alkyl,C₂-C₁₀-alkenyl, C₃-C₁₀-cycloalkyl, benzyl, C₆-C₁₄-aryl, eachunsubstituted or substituted one or more times with C₁-C₄-alkyl, benzylor phenyl, R³ is selected from hydrogen, COOR⁸, C₁-C₁₀-alkyl,C₂-C₁₀-alkenyl, C₃-C₁₀cycloalkyl, benzyl, C₆-C₁₄-aryl, eachunsubstituted or substituted one or more times with C₁-C₄-alkyl, benzylor phenyl, where R² and R³ may be the same or different, R⁴ and R⁵ arethe same or different and are each selected from hydrogen, C₁-C₁₀-alkyl,C₃-C₁₀-cycloalkyl, benzyl and C₆-C₁₄-aryl, each unsubstituted orsubstituted one or more times with C₁-C₄-alkyl, benzyl or phenyl, or>C(R⁴)₂ is a >C═O group, X, if present at all or in multiple occurrence,is the same or different and selected from oxygen, sulfur, N—R⁶ andC(R⁴)₂, where R⁶ is selected from C₁-C₁₀-alkyl, C₃-C₁₀-cycloalkyl,benzyl and C₆-C₁₄-aryl, each unsubstituted or substituted one or moretimes with C₁-C₄-alkyl, benzyl or phenyl, R⁷ in each occurrence is thesame or different and selected from hydrogen, C₁-C₁₀alkyl,C₃-C₁₀-cycloalkyl, benzyl and C₆-C₁₄-aryl, each unsubstituted orsubstituted one or more times with C₁-C₄-alkyl, benzyl or phenyl, R⁸ isselected from C₁-C₄-alkyl, n is an integer from 1 to
 3. 7. Theelectrochemical cell according to any one of claims 1 to 6 whereincompound of general formula (II) is selected as follows: R¹ in eachoccurrence is the same and selected from C₁-C₄-alkyl, C₁-C₄-alkoxy andphenyl, R² is selected from methyl, ethyl, isopropyl, tert-butyl andbenzyl, R³ is selected from hydrogen, methyl and ethyl.
 8. Theelectrochemical cell according to any one of claims 1 to 6 whereincompound of general formula (III) or (IV) is selected as follows:

R¹ in each occurrence is the same and selected from C₁-C₄-alkyl,C₁-C₄-alkoxy and phenyl, R² is selected from C₁-C₄-alkyl, COOCH₃,COOC₂H₅, C₂-C₃-alkenyl and phenyl, R⁷ is selected from hydrogen andmethyl.
 9. The use of electrochemical cells according to any one ofclaims 1 to 8 in lithium ion batteries.
 10. The use according to claim 9wherein a potential difference of at least 4.5 volts is reached betweenat least one anode and at least one cathode at least temporarily duringthe production and/or use of the electrochemical cell in question. 11.The use of electrochemical cells according to any one of claims 1 to 8for driving motor vehicles.
 12. The use of electrochemical cellsaccording to any one of claims 1 to 8 for energy storage in electricaltelecommunications equipment.
 13. A process for producingelectrochemical cells according to any one of claims 1 to 8, whichcomprises a cathode (A) and an anode (B) being combined with each otherin a receptacle and admixed with electrolyte (C).
 14. The processaccording to claim 13 wherein the admixing with electrolyte is precededby the internal pressure of the cell in question being lowered to valuesbelow 25 000 Pa (pascal).